1. Field of the Invention
The present invention relates to hearing aid amplifiers.
2. Description of Related Art
A hearing aid is typically comprised of a microphone which receives an acoustic input signal and converts it into an electrical signal, a filter which processes the signal, an amplifier which produces an amplified output signal, and a speaker which delivers the output signal.
With many hearing aid designs, especially those including Class D amplifiers, the amplifier will lose gain control under low battery conditions which may produce a loud squeal or gun shot noise. This may occur as the battery charge depletes with use, and also when a loud tone enters the hearing aid at a low frequency, causing the battery voltage to momentarily drop. Some hearing aids have been equipped with a latch which disables the hearing aid output when the amplifier oscillator frequency reaches a certain level. These prior art latches have not been completely effective, as latch activation can erroneously disable the hearing aid during a power supply transient in addition to a true low battery condition.